WASHINGTON (AP) —      It's not just what they say that matters in presidential debates.     The image of Mitt Romney laying a hand on Rick Perry's shoulder in the latest Republican debate may well be remembered long after people have forgotten what the two were squabbling over.     Classic moments from debates past often had more to do with what the candidates did than what they said.     President George H.W. Bush's words in a 1992 debate with Bill Clinton and Ross Perot are long forgotten. The fact that cameras caught the president checking his watch wasn't. It suggested to viewers that Bush wished he were someplace else.Supporters of Romney and Perry both tried to cast the latest debate dust-up in the best light for their candidates.